Biological materials may be preserved for long term storage by a number of techniques including storage at low temperatures and freeze-drying. Storage at low temperature, while effective, is limited to applications where constant refrigeration is available. The need for constant refrigeration limits the usefulness of this technique. Preservation of biological samples by freeze-drying, however, is not so limited.
The technique of freeze-drying, also known as lyophilization, involves the freezing of a sample, forming water crystals, followed by the direct sublimation of the water crystals, usually under vacuum. That is, the water is directly converted from a solid state to a gaseous state without passing through a liquid state. Freeze-drying, therefore, typically dehydrates a sample without denaturing or otherwise altering its three-dimensional structure by heating. Once freeze-dried, samples are often stable at room temperature for an extended period of time provided that the samples are stored in a water-vapor impermeable container, such as, for example, a glass ampule. Therefore, freeze-drying provides a method of long term storage of biological materials at room temperature.
Freeze-drying, however, has disadvantages associated with it. Freeze-drying requires both time and expensive equipment. Freeze-drying can also cause irreversible changes to occur in some proteins or other samples by mechanisms other than those associated with heating. Among these changes are denaturation caused by a change in pH or by the concentration of other substances near the molecules of the biological material. Therefore, there is a need for a method of preservation of biological materials that provides an alternative to freeze-drying. Such a need is acutely felt with regard to the delivery of biological materials to remote areas requiring long transport times with little or no refrigeration available. The delivery of vaccines or other medical products to remote areas is one specific example of such a need. Ideally, such a method would provide an economical method for long term preservation of such samples at room temperature.
The technique of electrostatic spinning, also known within the fiber forming industry as electrospinning, of liquids and/or solutions capable of forming fibers, is well known and has been described in a number of patents, such as, for example, U.S. Pat. Nos. 4,043,331 and 5,522,879. The process of electrostatic spinning generally involves the introduction of a liquid into an electric field, so that the liquid is caused to produce fibers. These fibers are generally drawn to a conductor at an attractive electrical potential for collection. During the conversion of the liquid into fibers, the fibers harden and/or dry. This hardening and/or drying may be caused by cooling of the liquid, i.e., where the liquid is normally a solid at room temperature; by evaporation of a solvent, e.g., by dehydration (physically induced hardening); or by a curing mechanism (chemically induced hardening). The process of electrostatic spinning has typically been directed toward the use of the fibers to create a mat or other non-woven material, as disclosed, for example, in U.S. Pat. No. 4,043,331. In other cases, electrospinning is used to form medical devices such as wound dressings, vascular prostheses, or neural prostheses as disclosed, for example, in U.S. Pat. No 5,522,879.
In still other cases, electrospinning is used to create fibers which act as a carrier for the delivery of therapeutic compounds, as disclosed, for example, in co-pending U.S. patent application Ser. No. 09/571444, filed on May 16, 2000. Such examples of electrospinning with therapeutic compounds involve immediate delivery of the electrospun material. Other uses of electrospinning to deliver therapeutic compounds have suggested the formation of a fiber which contains a core component and a coating component. In one example, provided in PCT/GB97/01968, a biologically active ingredient may be contained within a core of a fiber, fibril, or microcapsule. The active ingredient is released from the ends of the fiber or fibril, through the coating material if the coating material is permeable to the active component, or by enzymatic, physical, or chemical disruption of the coating, such as biodegradation or the application of pressure to the fiber. Such a fiber structure allows the biological material to remain in liquid form within the fiber. Such fibers may be used for a controlled release of the biologically active component. While electrospinning has been used to deliver therapeutic compounds, heretofore, electrospinning has not been used to preserve biological materials.
It is, therefore, an aspect of the present invention to provide a method of preserving biological material.
It is another aspect of the present invention to provide a method of preserving biological materials, as above, that is an alternative to freeze-drying.
At least one or more of the forgoing aspects, together with the advantages thereof over the prior art relating to the preservation of biological material, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
In general, the present invention provides a method of preserving biological material which includes the steps of providing at least one fiber-forming material, mixing at least one biological material, and optionally, one or more additives, to the at least one fiber-forming material to form a mixture, and forming a fiber from the mixture wherein the fiber has a diameter between about 0.3 nanometers and 25 microns.